Mechanical manipulator arms terminating in some type of mechanical hand or gripping device (end-effector) are commonly employed on space vehicles for performing planetary explorations, and satellite and space shuttle operations. The manipulator arms and the joints thereof together with the end-effector are usually remotely controlled by a closed-loop guidance system commonly known as a teleoperator. Teleoperators normally include a guidance loop having an electronic eye device such as stereo television and a man in the loop to remotely control the manipulator arm and hand through motorized pivot joints.
During the past several years an increased effort in manipulator design has been directed mainly toward the actual control of the manipulator with or without the attached end-effectors in order to perform special tasks from a remote position. As important as this research is, it should be realized that the degree of control sophistication is directly proportional to the degree of manipulator joint and end-effector sophistication.
It seems that enough effort has not been directed to the design and improvement of the various joints, their drives and their configurations. The practice of present day equipment-designers seems to point to the separation of yaw, pitch and roll motion by physical distances, especially in the wrist joint located at the terminal end of the manipulator arm upon which the end-effector is carried. This practice makes the solution of the mathematical equation, which defines the relative position of the terminal end of the manipulator and which is utilized in the control system, a rather difficult task.
Also, past joint designs have resulted in several configurations of acceptable, small physical shape but which show externally applied drive and several mechanisms. These devices thus nullify the objective of improved visibility around the joint.
For space application the joints with bulky configurations cannot be accepted since many tasks will have to be performed in the "shadow-side" and requiring illumination from sources on the teleoperator. These requirements demand a maximum of visibility.
In many present day designs of manipulator arms the wrist joint configuration has been simplified to the degree that not three but two motions occur in the wrist joint whereas the third motion is supplied by the shoulder of the manipulator arm or is completely ignored altogether. For those arms that have three degrees of freedom in the wrist joint, the actual configurations produce, in some cases, a very bulky joint which does not provide for the required visibility referred to above.
The task at present is to design a wrist joint assembly which is better than what is currently available yet conforms to the rules of sound kinematic manipulator design. The present invention provides such a new device which has been successfully demonstrated.